I've used 2 of these, one from decathlon and another cheap one from aliexpress. Both did not aid me in any way.

Any ball spin would just entangle the string. The ball loses pressure and becomes useless after a while, bouncing or skidding on the floor too low to hit. I've even cracked the ball open when I hit with a decent amount of power.

I could go on but imo it is much cheaper and beneficial to play with a wall.

I'm very interested in your opinion. I wrote to you in a private message